In order to control a passage or blocking of a traffic to flow through a network, a firewall (FW) is provided at a coupling point between networks in some cases.
The FW is provided in a sub-network at, for example, a company office or the like coupled to a wide area network (may be called a “core network”), in some cases. The FW causes only desired traffics to pass from the core network to the sub-network and discards other traffics, thereby enabling the security of the sub-network to be enhanced. Note that the “traffic” may be called a “data flow” or simply called a “flow”. As documents of the related art, there are Japanese Laid-open Patent Publication No. 2015-91106, Japanese Laid-open Patent Publication No. 2014-236461, Japanese National Publication of International Patent Application No. 2008-508805, Japanese Laid-open Patent Publication No. 2006-254137, and Japanese Laid-open Patent Publication No. 2014-230157.